Tire Rolling Circumference

[Johan Bornman]

Cut cut cut cut

 

JB' date=' I have noticed that the 25 c seems to have more tyre (If I can put it that way.) between the road and the rim. 23 c's by comaprison seem to be lower profile than 25 c's.

 

At my weight of now 91 kg, the 25 c is a little more comfortable and I prefer the overall feel of the ride on 25's.

 

I was checking out the "table" and the closest measurements in the 700 range is the 700 X 20C.  Made a mistook a while ago and bought a 20c tube. Dam thing was so skinny it popped inside my 23c tyre when I was inflating it. Fortuantely no damage to anything other than tube.

 

We live and learn. Now I check the boxes and the contents. Some jokers like to switch stuff around in those boxes on the shelves.

[/quote']

The reason there is more tyre between rim and road on the 28 than the 25 is because the perfectly tubular pipe is 3mm bigger in diameter. In other words, the big tyre is 3mm further off the road. That should be obvious.

 

As for the 20mm tube bursting inside your 23mm tyre. Something is not quite halaal in this mixed grill.

 

1) A tube will NEVER burst inside a tyre. It has to be outside a tyre to burst. If it splits or fails inside a tyre it makes a pffffft sound, not a bang. Maybe your pop was a pffft.

 

2) Tubes expand to fill just about any tyre other than a Harley's rear tyre. A 20mm tube will easily work inside a 32mm tyre. If it had failed inside a tyre it failed for reasons other than size. The whole issue of 23mm or 20mm tubes is hogwash. One size fits all (within reason).

 

 

 

 

 

[Slave]

Ah, we live and learn. JB, you are a mine of useful information.

 

Once again, this proves that the assumption is the fother of all muck-ups.

 

Car tyres (yeah, I know big diffs, four wheels etc, etc.) the size designates width, profile and rim size. So a 175X65X14 is 175 mm wide, has a profile of 65% of tyre width and fits a 14 inch rim.

 

I, very stoopidly assumed, that bike tyres would be about a similar thing. Based on the 27X1 and 1 quarter size and theory. So, based on this ridiculous assumption, I assumed that 23c and 25 c tyres would have referred to the width of the tyre,while 700 refers to rim size / diameter or some other as yet unkown criteria. 

 

All is good though, I learned stuff. See, I am just like a computer. You have to punch data into me.

 

Edit; BTW, JB, the sound was somewhere between a pfffft and the sound of a peanut butter sarmie landing flat on the tiled (and freshly washed) kitchen floor.

 

Tube split along one of the seams. (damn cheap "made in china" junk.'nuff said).

Slave2Love2009-02-24 03:07:38

[Slave]

Experiment results. (I measured various tyres on Teeny's and my bike last night.)

 

Teeny has a Vottoria 23c tyre on back and Conti Sport 25c on Front.

 

I have bonts back and front. Both 25C

 

Tyre make      Size          Loaded                  Unloaded

Vitoria            23c           2076                      2104

Conti              25c           2090                      2101

Bont               25c           2078                      2106

 

Based on this, I assume then that the Cateye and possiby other cycle computer manufacturers use 2105 as the default measurement because it is pretty close to being standard onmost unloaded tyres.

 

I know that rider weight and tyre pressure will have an effect on the overall rolling circumference and the difference therein. I guess that my tyres have deflated some since I did the measurement on Sunday. (Almost 100 k's on the road.)

 

I found it interesting though that a 23c and 25c had very little difference on the unloaded tyre measurement.

 

JB. Feel free to comment.